$ curl /v3/route_mappings -X POST -d '{
  "relationships": {
    "app": {
      "guid": "a4238936-3f25-463b-4061-d3436e277be3"
    },
    "route": {
      "guid": "83d60b98-5864-45c6-94ad-4d02f5f4216a"
    }
  },
  "weight": 2
}'